Go Green, Go Online to take your coursePublication Date: June 2007Review Date: December 2010Expiry Date: November 2013

This course has been made possible through an unrestricted educational grant. The cost of this CE course is $49.00 for 2 CE credits. Cancellation/Refund Policy: Any participant who is not 100% satisfied with this course can request a full refund by contacting PennWell in writing.

Earn2 CE creditsThis course was

written for dentists, dental hygienists,

and assistants.

Functional Anatomy and TM PathologyA Peer-Reviewed Publication Written by Steven R. Olmos, DDS

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Educational ObjectivesUpon completion of this course, the clinician will be able to do the following:1. Describe the functional anatomy of the temporoman-

dibular joint (TMJ). 2. List and describe what makes the TMJ a unique joint.3. Describe TMJ pathology.

AbstractTMJ anatomy comprises the bones, ligaments, tendons and muscles of the region. Up to 75 percent of the population has at least one sign or symptom of temporomandibular dysfunc-tion and 34 percent report having this. An understanding of the bones, ligaments, tendons, muscles, joint spaces, articular disc, synovial tissues and fluids, and the role of proteoglycans is necessary to understand the factors involved in TMJ health and disease.

IntroductionUp to 75 percent of the population has at least one sign or symptom of temporomandibular (TM) dysfunction at any given time, and 34 percent of the population reports having a temporomandibular disorder (TMD).1 Understanding and treating TMDs is an opportunity to help up to one-third of patients.

TM dysfunction and sleep-disordered breathing are un-der-diagnosed and under-treated. Amongst physicians who are not sleep specialists, only 24 percent screen for obstructive sleep apnea.

TM dysfunction is an orthopedic problem. There must be a team-oriented focus that includes specialists from multiple disci-plines. According to Dr. Peter Dawson, “There is a primary tenet that embraces the entire subject of occlusion from the TMJs to smile design. It is that the teeth are but one part of the masticatory system, and if the teeth are not in equilibrium with all the other parts of the total system, something is likely to break down.” A healthy joint is a pre-requisite for successful restorative work. It is imperative that dental professionals understand how to identify and properly treat TMDs and know when to refer.

Anatomy of the TMJ is complex and important in under-standing the pathology and treatment of TMDs. This article is intended as a refresher on TMJ anatomy and pathology.

Anatomy of the temporomandibular joint The TMJ is the most complex joint in the body. It provides for hinging movement in one plane (a ginglymoid joint), and at the same time provides for sliding movements (an arthrodial joint). Therefore, it is technically a ginglymoar-throdial joint. The TMJ is classified as a compound joint i.e., requiring the presence of at least three bones.

The articular disc is composed of dense fibrous con-nective tissue devoid of any blood vessels or nerve fibers. Functionally it serves as a non-ossified bone that permits the complex movements of the joint. The articular disc can

be divided into central, anterior and posterior regions. The central area, the intermediate zone, is the thinnest. The an-terior border is generally slightly thinner than the posterior border. From an anterior view, the disc is generally thicker medially than laterally, which corresponds to the increased space between the condyle and the articular fossa toward the medial aspect of the joint. On opening, the superior surface of the articular disc has a sigmoid shape. The disc is firmly attached downward to the medial and lateral poles of the condylar head. The disc is the primary storage site for synovial fluid.

Articular Disc

Retrodiscal tissuePosterior band

Intermediate zoneAnterior band

Articular Disc

Retrodiscal Tissue

Retrodiscal tissue

The retrodiscal tissue, or posterior attachment, consists of an area of loose connective tissue that is attached to the posterior aspect of the articular disc. It is highly vascularized and innervated, and is bordered superiorly by the superior retrodiscal lamina.

The superior retrodiscal lamina consists of connective tissue containing many elastic fibers. It attaches the articu-lar disc posteriorly to the tympanic plate. Its function is to counter the forward pull of the superior belly of the lateral pterygoid muscle on the articular disc. When the mouth is fully opened, the retrodiscal tissue is fully stretched. The superior retrodiscal lamina prevents the disc from dislocat-ing anteriorly, and also results in posterior rotation of the meniscus — allowing the thin intermediate portion of the disc to remain between the articular surfaces of the condyle and eminence.

The inferior retrodiscal lamina consists mainly of collag-enous fibers. It is located at the lower border of the retrodiscal tissues. It attaches the inferior border of the posterior aspect

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of the disc to the posterior margin of the articular surface of the condyle.

Posteriorly, the remaining body of the disc is attached to a large venous plexus that fills with blood as the con-dyle moves forward. Anteriorly, the superior and inferior aspects of the disc are attached to the capsular ligament, which surrounds most of the joint. The superior and infe-rior attachments are to the anterior margins of the articular surface of the temporal bone and condyle respectively. The disc is also attached by tendinous fibers to the superior lateral pterygoid muscle, between the attachments of the capsular ligament.

Fibrous Connective TissueThe articular disc is attached to the capsular ligament an-teriorly and posteriorly, as well as medially and laterally. This divides the joint into two distinct cavities. The internal surfaces of the cavities are surrounded by specialized endo-thelial cells that form a synovial lining. This lining, along with a specialized synovial fringe located at the anterior border of the retrodiscal tissues, produces synovial fluid that fills both joint cavities.

The articular surfaces of the mandibular fossa and condyle are lined with dense fibrous connective tissue rather than hyaline cartilage, as in most other mobile joints. The fibrous connective tissue in the joint affords several advantages over hyaline cartilage; it is generally less susceptible to the effects of aging and therefore less likely to break down over time, and has a much greater ability to repair.

BonesThe TMJ is composed of the condyle (mandible) and the articular (or glenoid) fossa of the temporal bones, bilaterally. The temporal bone consists of five parts: squamous, petrous, internal acoustic meatus, zygomatic, and middle cranial fossa. The facial nerve (motor control over the facial muscles) and the vestibulocochlear nerve (balance and hearing) both travel the course of the internal acoustic meatus. The middle cranial fossa is the floor, which supports the brain stem from which the cranial nerves originate.

Articular, or glenoid, fossa

The connection between the TMJ and the middle ear is through the petro-tympanic fissure. This runs the length of the glenoid fossa.

The condyle may have several different normal shapes. The shape should be the same right to left. A flat condyle surface on one side may be pathologic if the contra-lateral side is angled. Condyles that are both angled or both flat may be normal contours.

Convex Flat

Angled Round

Synovial JointThe TMJ is referred to as a synovial joint. The articular disc is the primary source of synovial lubricant within the TMJ. The synovial fluid acts as a medium for providing metabolic re-quirements to these tissues. There is free and rapid exchange between the vessels of the capsule, the synovial fluid, and the articular tissues. The inferior joint space contains about 0.9 ml of synovial fluid, and the superior joint space contains about 1.2 mL of synovial fluid. The synovial fluid also serves as a lubricant between articular surfaces during function. The articular surfaces of the disc, condyle, and fossa are very smooth — this minimizes friction during movement. The synovial fluid helps to further minimize this friction.

Inferior Joint Space

Inferior joint space

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This lies on the condylar head like a cap and drapes over all surfaces, but extends most caudad to the condylar neck in its posterior aspect. When the mandible is depressed, the in-ferior joint space opens to a greater extent posteriorly, giving the appearance in lateral view of a teardrop in the inferior joint space posterior to the condylar head. The anterior portion of the inferior joint space forms a small fossa where the fibers of that capsular ligament and the anterior band of the disc form a concretion. This sling-like structure helps to stabilize the disc against the condylar head during function.

Superior Joint Space

Superior joint space

This is larger and more anteriorly placed than the infe-rior joint space. Its shape in the cephalad aspect corresponds closely to the glenoid fossa. On the caudad aspect, the concav-ity of the intermediate zone can be noted. The separation of the retrodiscal tissue from the posterior band is clearly dif-ferentiated when viewed from the superior joint space. The anterior fossa of the superior joint space forms a concavity in front of the condylar head. The medial fossa forms a concav-ity medial to the condylar head.

The precise shape of the disc is determined by the morphology of the condyle and mandibular fossa. During movement, the disc is somewhat flexible and can adapt to the functional demands of the articular surfaces. However, flex-ibility and adaptability do not imply that the morphology of the disc is reversibly altered during function. The disc main-tains its morphology unless destructive forces or structural changes occur in the joint.

Synovial MembraneThe joint is enclosed by a fibrous capsule, which is lined by a synovial membrane. This membrane is highly vascular and is continuous with the connective tissue of the capsule. Both upper and lower joint compartments are lined with their own synovial membrane.

The synovial membrane allows diffusion of a plasma filtrate and components of its own to produce synovial fluid that fills both joint compartments. Its shape is altered during functional movement. The largest area of synovial tissue is on the superior and inferior retrodiscal lamina, where it forms small folds, or villi, that stretch on translation of the condyle and disc. The articulating surfaces of the temporal bone, the condyle, and the disc are not covered.

The synovial tissue can be divided into three layers:1. The synovial lining, or intima, is the most intimate with

the functional joint surfaces.2. The subsynovial tissue, which is similar to the intima but

with a more developed connective tissue network.3. The capsule, which is a relatively acellular layer with

thick bands of collagen that forms the outer boundary of the joint.

Synovial surfaces are nonadherent. The cells on the surface bind to the underlying matrix but not to the opposing tissue. Constant movement against opposing surfaces is thought to break down any forming cross-links. Collagenase secretion by the synovial lining cells also helps prevent the formation of surface adhesions and ensures that fragmented collagen on the tissue surface does not activate the coagulation cascade.

Synovial tissue has the ability to regenerate when dam-aged. Synovial fluid is a filtrate of plasma that passes through fenestrations in the sub-endothelial capillaries into the inter-cellular spaces. Because there is no epithelium, and hence no basement membrane, no barrier exists between the synovium and the fluid present in the joint spaces. Movement is mainly by passive diffusion.

ProteoglycansThese are within the articular tissues on the anterior part of the condyle, in the central part of the disc, and on the lateral portion of the articular eminence.

Hyaluronic acid Monomer

Interstitial fluid

Collagen fibril

40 nm

Attached monomer

The presence and amount of proteoglycans, specifically glycosaminoglycans (GAGs) relative to the collagen matrix in articular tissues is a measure of the resilience of the tis-sue and, therefore, determines the amount of compressive loading that the joint can withstand. Proteoglycans are mac-romolecules found in all connective tissues and extracellular matrices and on the surface of many cells. They contain a core protein to which one or more GAG polysaccharide chains are covalently bonded.

Glycosaminoglycans In sufficient concentration glycosaminoglycans (GAGs) cause the cartilage tissue to imbibe extracellular water, thus produc-

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ing a cushion to compressive loads. The flexible, hydrophilic nature of the GAG chains and their high concentration of negatively charged fixed groups leads to a high swelling pres-sure, while the fine macromolecular mesh of collagen ensures a low hydraulic permeability. GAGs are ideal as a load-bear-ing material with low surface coefficient of friction.

A reduction in collagen concentration or an increased dis-order in collagen orientation would lead to a decrease in the degree of cartilage reinforcement and also an increase in local hydraulic permeability. The three requirements for healthy cartilage are:1. Plenty of water for diffusion of nutrients and

for lubrication. 2. Proteoglycans, which, due to their anionic nature, are

tremendously hydrophilic, thus serving to attract and maintain water molecules.

3. A collagenous mass in which these proteoglycans can bind.

Boundary and Weeping LubricationSynovial fluid lubricates the articular surfaces by way of two mechanisms: boundary lubrication and weeping lubrication.

Boundary lubrication occurs when the joint is moved and synovial fluid is forced from one area of the cavity into another. The synovial fluid located in the border re-gions is forced upon the articular surface, thus providing lubrication. Boundary lubrication prevents friction in the moving joint.

Weeping lubrication refers to the ability of the articular surfaces to absorb a small amount of synovial fluid. When the articular surfaces are placed under compressive forces, this small amount of synovial fluid is released. Weeping lu-brication helps eliminate friction in the compressed but not moving joint. Only a small amount of friction is eliminated as a result of weeping lubrication and prolonged compressive forces to the articular surfaces will exhaust this supply.

LigamentsThe function of ligaments is to hold the skeleton together. Ligaments attach to bone and are made up of collagenous connective tissue, which does not stretch. They act as passive restraining devices to limit and restrict joint movement. They prevent joint laxity. They transfer tensile strength from bone to bone. They are virtually identical to tendons. They have a poor vascular supply.

The three functional ligaments that support the TMJ are:1. The collateral ligaments.2. The capsular ligament.3. The temporomandibular ligament.

The two accessory ligaments of the TMJ are: 1. The sphenomandibular ligament.2. The stylomandibular ligament.

Collateral (Discal) Ligaments

Superior joint

Inferior joint

Lateral discal

Capsular ligament

Articular disc

Medial discal

Capsular ligament

The collateral, or discal, ligaments attach the medial and lateral borders of the articular disc to the poles of the condyle. The medial discal ligament attaches the medial edge of the disc to the medial pole of the condyle. The lateral discal liga-ment attaches the lateral edge of the disc to the lateral pole of the condyle.

The collateral ligaments are true ligaments, composed of collagenous connective tissue fibers, and therefore do not stretch. They divide the joint mediolaterally into the superior and inferior joint cavities. They function by restricting move-ment of the disc away from the condyle and causing the disc to move passively with the condyle as it glides anteriorly and posteriorly. These ligaments permit the disc to be rotated an-teriorly and posteriorly on the articular surface of the condyle, and are responsible for the hinging movement of the TMJ. They are vascularly supplied and are innervated; this in-nervation provides information regarding joint position and movement. Strain on these ligaments produces pain.

Capsular Ligament

The entire TMJ is surrounded and encompassed by the capsular ligament. The fibers of the capsular ligament are attached superiorly to the temporal bone along the borders of the articular surfaces of the mandibular fossa and the articular eminence.

Inferiorly, the fibers of the capsular ligament are attached to the neck of the condyle. The capsular ligament acts to resist any medial, lateral, or inferior forces that tend to separate or dislocate the articular surfaces. A significant function of the capsular ligament is to encompass the joint, thus retaining the synovial fluid. The capsular ligament is well innervated

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and provides proprioceptive feedback regarding position and movement of the joint.

Temporomandibular Ligament

The lateral aspect of the capsular ligament is reinforced by strong, tight fibers that make up the lateral ligament or the temporomandibular ligament. The temporoman-dibular ligament is composed of two parts:1. The outer oblique portion, which extends from the

outer surface of the articular tubercle and zygomatic process posteroinferiorly to the outer surface of the condylar neck.

2. The inner horizontal portion, which extends from the outer surface of the articular tubercle and zygomatic process posteriorly and horizontally to the lateral pole of the condyle and posterior part of the articular disc.

The oblique portion of the TM ligament resists exces-sive dropping of the condyle and therefore limits the ex-tent of mouth opening. This portion of the ligament also influences the normal opening movement of the mandible. During the initial phase of opening, the condyle can ro-tate around a fixed point until the TM ligament becomes tight as its point of insertion on the neck of the condyle. When the ligament is taut, the neck of the condyle can-not rotate further. If the mouth were to be opened wider, the condyle would need to move downward and forward across the articular eminence.

The inner horizontal portion of the TM ligament limits posterior movement of the condyle and disc. When force applied to the mandible displaces the condyle pos-teriorly, this portion of the ligament becomes tight and prevents the condyle from moving into the posterior re-gion of the mandibular fossa. The TM ligament protects the retrodiscal tissues from trauma created by the pos-terior displacement of the condyle. The inner horizontal portion also protects the lateral pterygoid muscle from over-lengthening or extending.

Sphenomandibular Ligament This arises from the spine of the sphenoid bone and ex-tends downward to a small bony prominence on the medial surface of the ramus of the mandible called the lingula. It does not have any significant limiting effects on mandibu-lar movement.

Stylomandibular ligament

Sphenomandibular ligament

Stylomandibular Ligament The second accessory ligament is the stylomandibular liga-ment. It arises from the styloid process and extends down-ward and forward to the angle and posterior border of the ramus of the mandible. It becomes taut when the mandible is protruded and is most relaxed when the mandible is opened. The stylomandibular ligament therefore limits excessive pro-trusive movements of the mandible.

TendonsTendons are the connective tissues that attach muscle to bone. They are composed primarily of collagen. Tendons are nonelastic but flexible. They have a poor vascular supply. Ten-dons are attached to bone via either periosteum or fasciculi of fibers (Sharpey’s fibers). Their tensile strength is similar to bone (i.e., half that of steel). Golgi tendon organs are tension sensors located in the tendons. Some tendons are contained within a synovial sheath (e.g., tensor veli palatini). Tendons heal in two stages: 1. A scar or callus (disorganized collagen) forms, which

may take up to five weeks.2. The scar is remodeled and replaced with new collagen,

which may take up to three years.

Muscles of the Cranial Mandibular RegionThe position of the mandible and its craniomandibular ar-ticulation in space are mainly determined by the activity of the 27 muscles that attach the jaw.

Muscles of Mastication

Elevators

Origin: The temporal fossa and the lateral surface of the skull.

Insertion: The lateral head inserts on the lateral surface of the coronoid process, and the medial head attaches to the medial surface of the ascending ramus down to the level of the third molars.

Function: This muscle is divided into three distinct areas according to fiber direction and ultimate function. The anterior portion consists of fibers that are directed

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almost vertically. The middle portion contains fibers that run obliquely across the lateral aspect of the skull (slightly forward as they pass downward). The poste-rior portion consists of fibers that are aligned almost horizontally, coming forward above the ear to join other temporalis fibers as they pass under the zygomatic arch. When the anterior portion contracts, the mandible is raised vertically. Contraction of the middle portion will elevate and retrude the mandible. Because the angula-tion of its muscle fibers varies, the temporalis is capable of coordinating closing movements. It is a significant positioning muscle of the mandible.

Innervation: Cranial nerve 5 (trigeminal nerve), division III.

Shape: Fan-shaped.Clinically: If the mandible is in the incorrect position

(condyles displaced posteriorly), this muscle will be aggravated and will contract excessively. Eventually, trigger points will form.

Masseter Muscle

Origin: a) Superior portion: Anterior two-thirds of the lower

border of the zygomatic arch. b) Deep portion: Medial surface of the

zygomatic arch.Insertion: Its insertion on the mandible extends from the

region of the second molar at the inferior border poste-riorly to include the angle. It is made up of two heads:

the superficial portion (A) consists of fibers that run downward and slightly backward, and the deep portion (B) consists of fibers that run predominantly vertically. Together they attach to the lateral surface of the ramus of the mandible and the coronoid process.

Shape: Rhomboidal.Function: As fibers of the masseter contract, the mandible

is elevated and the teeth are brought into contact. The masseter is a powerful muscle that provides the force necessary to chew efficiently. Its superficial portion may also aid in protruding the mandible. When the mandible is protruded and biting forces are applied, the fibers of the deep portion stabilize the condyle against the articular eminence.

Innervation: Cranial nerve 5 (trigeminal nerve), division III.

Clinically: This muscle contracts excessively and forms trigger points in patients who have noxious habits such as bruxing or clenching. The masseter is also aggravated if the patient has a skeletal closed bite, deep dental overbite, lack of adequate vertical dimension, or short lower face height, which causes the muscles to shorten.

Depressors

Lateral Pterygoid

Superior and Inferior Head Origins: a) Infratemporal surface of the greater wing of the

sphenoid bone. b) Lateral surface of the lateral pterygoid plate.Insertion: a) Articular disc. b) Neck of the condyle.Function: When the right and left inferior lateral pterygoids

contract simultaneously, the condyles are pulled down the articular eminence and the mandible is protruded. When this muscle functions with the mandibular depres-sors, the mandible is lowered and the condyles glide forward and downward on the articular eminence. The superior lateral pterygoid is considerably smaller than the inferior. Whereas the inferior lateral pterygoid is active during opening, the superior remains inactive, becoming active only in conjunction with the elevator muscles. The

Temporalis Muscle

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superior lateral pterygoid is especially active during the power stroke and when the teeth are held together. The power stroke refers to movements that involve closure of the mandible against resistance, such as in chewing. When this muscle is active, the disc is pulled anteriorly and medially.

Innervation: Cranial nerve 5 (trigeminal nerve), division III.

Clinically: a) If the patient has a deep overbite, the lateral

pterygoids will be overworked as the patient goes through lateral excursions.

b) It has been reported that 5 percent of the fibers of the superior head of the lateral pterygoid attach behind the eye. This certainly would account for some of the retro-orbital pain that some TMJ patients experience.

Medial PterygoidThe lateral pterygoid plate separates the lateral pterygoid from the medial pterygoid.

Origin: Medial surface of the lateral pterygoid plate, pyra-midal process of the palatine bone, maxillary tuberosity.

Insertion: Posterior and lower part of medial surface of ramus and angle of mandible.

Function: Protracts and elevates the mandible. Assists in the rotary movements of the mandible.

Shape: Rhomboidal.Clinically: This muscle is frequently sensitive in patients

with TMJ dysfunction, so palpate gently.

Anterior and Posterior Digastric

Posterior belly

Anterior belly

Origin: a) Posterior belly: Mastoid notch of temporal

bone, just medial to the mastoid process. b) Anterior belly: Digastric fossa of the man-

dible, just above the lower border and close to the midline.

Insertion: a) Posterior belly: Fibers run forward, downward,

and inward to the intermediate tendon attached to the hyoid bone.

b) Anterior belly: Fibers extend downward and backward to insert at the same intermediate tendon as does the posterior belly.

Function: When the right and left digastric muscles contract and the hyoid bone is fixed in position by the suprahyoid and infrahyoid muscles, the mandible is depressed and pulled backward and the teeth are brought out of contact. When the mandible is stabilized, the digastric muscles, with the suprahyoid and infrahyoid muscles, elevate the hyoid bone (a necessary function for swallowing). The digastrics are among many muscles that depress the mandible and raise the hyoid bone. Generally, muscles that are attached from the mandible to the hyoid bone are called suprahyoid, and those attached from the hyoid bone to the clavicle and sternum are called infrahyoid. The supra- and infrahyoid muscles play a major role in coordinating mandibular function.

Innervation: a) Posterior belly: Cranial nerve 7 (facial nerve). b) Anterior belly: Cranial nerve 5 (trigeminal

nerve), mylohyoid nerve.Clinically: Most Class II skeletal patients have

retrognathic mandibles, and the posterior digastric is extremely sensitive in most of these patients. The clinician must be extremely careful when palpating this muscle.

Features That Are Unique to the Temporomandibular JointThere are several distinguishing features that are unique to the TMJ:1. It is a bilateral diarthrosis; the left and right sides must

function together. 2. The articulating surfaces are covered with fibrocartilage

rather than hyaline cartilage.3. The TMJ is the only joint in the human body to have

a rigid endpoint of closure, that of the teeth making occlusal contact. Translation occurs in the superior joint space, and rotational movement occurs in the lower, or inferior, joint space.

4. The TMJ is the last joint to start development, beginning at about seven weeks in utero, and develops from two distinct blastomas.

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Pathology of Temporomandibular Joint DisordersThe term “temporomandibular disorders” (TMD) was defined by the American Dental Association (ADA) in 1982 as “characterized by regional signs and symptoms, including pain in the area of the TM joint and/or masticatory muscles, often with limited mandibular range of motion, and/or TM joint sounds (clicking and/or crepitus)”. The ADA position of pathogenesis states: “The causes of TMD, and why some patients develop chronic, persistent symptoms, are not well understood”.2 The ADA feels that the most reasonable clini-cal diagnostic classification is that published by the American Academy of Orofacial Pain by Okeson, 1996.”3

Orofacial pain as described by Okeson includes: “pain conditions that are associated with the hard and soft tissues of the head, face, neck, and all of the intraoral structures. The diagnostic range includes headaches, musculoskeletal pains, neurogenic pains, psychogenic pains, and pains from major diseases such as cancer and acquired immunodeficiency syn-drome (AIDS).”4

Etiology of TMDsTMDs result from the various types of trauma. Macro-trauma (direct trauma) is injury due to impact or extensive stretching, twisting, or compression of the mandible. It is due to sudden force and may result from indirect trauma such as acceleration-deceleration injury (whiplash). Mi-crotrauma occurs as a result of sustained and repetitious adverse loading or continued compression due to parafunc-tional oral activities (clenching and grinding). This form of trauma is likely due to failure of the collagen matrix of the disc through a fatigue-like mechanism. Forward head pos-ture has been found to be a contributing factor that leads to joint strain and musculoskeletal pain, including headache, in the TMD patient.5

Degenerative changes and stages of intra-capsular pathologyDegenerative changes may result in cartilage debris being found within the joint, following local inflammation of the lateral capsule, or the posterior joint space (retro-discitis). Inflammation of the joint capsule can be the result of un-resolved ligamentous and tendinous insertion injuries due to traumas.6 “Capsulitis (inflammation of the outer fibrous layer of the joint capsule) and synovitis (inflammation of the inner synovial lining) have almost the same clinical char-acteristics and are usually considered as one clinical entity. Both conditions may occur secondary to compressive trauma to the TMJ, after prolonged mouth opening, or after sudden stretching or sprain of capsular or discal ligaments. Capsu-litis and synovitis may be associated with other coexisting TMJ disorders such as a disc displacement, hypermobility, or dislocation. It is not unusual to find degenerative cartilage debris within the joint.”7

Normal disc movementWhen the mouth is opened the condyle rotates and, at the same time, moves down the posterior slope of the articular eminence. The superior head of the lateral pterygoid muscle then moves the disc forward. This enables the disc to remain between the two bones, thus providing a cushion which keeps the two bones from rubbing together. As the jaw closes, the condyle moves back up into the glenoid fossa and the disc fol-lows, being guided by the lateral ligament.

The biconcave shape of the disc, which is thicker at both ends, helps keep the disc in its proper relationship on the head of the condyle during opening and closing of the jaw. When the disc remains in its proper position, no popping or clicking sound occurs.

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Joint noiseWhen the jaw opens and closes, there should be no noise. If a joint makes a noise, there is friction within the joint. This usually means that the disc is out of position anteriorly when the patient opens and closes in centric occlusion (biting on the posterior teeth). There should be no clicking, popping or grinding noises emanating from the joint when the jaw moves. Joint sounds may vary from a soft pop or clicking sound to a loud pop, or they can come in the form of rustling sounds like the crumpling of newspaper.

Open lockOccasionally, when the jaw is opening the disc may move too far forward and get caught over the anterior slope of the emi-nence. This is called an open lock and will result in the patient having difficulty closing his or her mouth. To treat this, place your fingers inside the patient’s mouth buccal to the lower posterior teeth and with your thumb on the chin, push the jaw slightly downward and backward. This will move the condyle and disc from underneath the anterior slope of the eminence and, hopefully, restore the joint to normal function. Care should be taken not to place your fingers between the teeth during this procedure since there is a strong reflex action that can occur when the jaw snaps back into its normal position.

Disc displacement with reductionAn accident or incorrect jaw position (condyle located too far posteriorly or superiorly) results in damaged or stretched posterior lateral ligaments. This allows the disc to become anteriorly or antero-medially displaced in relation to the head of the condyle. As the jaw opens, the disc is located in front of the condyle and a click occurs when the condyle snaps back into position beneath the disc.

Disc displacement with reduction means that when the jaw is opened and the condyle moves downward and forward, the disc is reduced or, in other words, recaptured and goes back to its proper position on the head of the condyle. In this position, it functions as a cushion or shock absorber between the articular eminence of the temporal bone and the head of the condyle during the opening cycle of the jaw. However, as the mouth closes into centric occlusion, shortly before closure the condyle slips off the disc, creating a soft closing click or pop. This is known as the reciprocal click.

Clicking sounds which occur as the jaw is just beginning to open are called early opening clicks and are usually less of a problem and easier to treat than clicks which occur at maxi-mum opening. In the case of early opening clicks, the disc has not slipped very far out of position. Therefore, we can assume that the ligaments holding the disc in position have not been stretched too severely and the disc can be recaptured during the opening cycle. Patients with early opening clicks respond well to anterior repositioning appliances that are designed to move the condyle down and forward so that the disc can be recaptured to its normal position on the head of the condyle.

Disc displacement with reduction

1. Jaw ClosedDisc displaced anteriorly

2. Jaw OpeningDisc displaced anteriorly

3. Disc Recaptured Click

4. Maximum Opening Disc recaptured

5. Jaw ClosingDisc recaptured

6. ClickReciprocal ClickDisc Displaced anteriorly

7. Jaw ClosedDisc displaced anteriorly

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Disc displacement without reductionIn cases with disc displacement without reduction, the poste-rior lateral ligaments have been severely stretched. These liga-ments are designed to hold the disc on the head of the condyle. If the ligaments are severely stretched, when the jaw opens they are unable to pull the anteriorly displaced disc back onto the head of the condyle. When it is impossible to recapture the disc and return it to its normal position on the head of the condyle during jaw opening and closing movements, this is referred to as disc displacement without reduction. While the ideal situation would be to recapture the disc, some patients respond well to anterior repositioning appliances. If the pos-terior lateral ligaments are stretched and not perforated, they may become fibrotic over time following anterior reposition-ing of the condyle and the patient may function quite well on what is then termed the pseudodisc.

Acute closed lock (intermittent locking)Most temporomandibular dysfunction patients tend to worsen with time. Slight clicking progresses to more frequent clicking and then eventually to jaw locking. This is due to the posterior ligaments continuing to stretch, allowing the disc to slip further and further out of position. Eventually, when the disc slips out of position too far anteriorly or antero-medially, the jaw will lock shut. This condition is known as a closed lock. When this first occurs it is known as an acute closed lock, and the patient reports that they heard a loud pop and could not open their mouth. The patient experiences a great deal of pain and limited jaw opening ranging between one-quarter and one-half inch.

Treatment involves trying to decompress the TM joints as soon as possible. The problem is that the patient cannot open his or her mouth wide enough to take an impression of the teeth in order to fabricate a hard acrylic splint.

In these cases, a temporary soft splint called an Aqualizer can be used. This allows for a slight separation of the teeth and will hopefully help move the condyle downward and forward so that there will be enough room for the disc to return to its normal position between the head of the condyle and the pos-terior slope of the articular eminence. Once the muscles have relaxed and the patient can open his or her mouth normally, a lower diagnostic splint (hard acrylic) is fabricated to help prevent the acute closed lock from recurring.

Chronic closed lockA patient with chronic closed lock has had the prob-lem longer than six months. The disc is permanently dislocated anteriorly or antero-medially to the condyle during opening and closing of the jaw. The disc is never positioned between the bones during the opening and closing cycle. If the patient is not treated within the first few weeks, the disc will begin to degenerate and lose its shape and the patient will gradually begin to open wider and wider as the disc is slowly destroyed. Once the disc is

Disc displacement without reduction

1. Jaw ClosedDisc displaced anteriorly

2. Jaw OpeningDisc displaced anteriorly

3. Disc CompressedDisc displaced anteriorly

4. Maximum Opening Disc displaced anteriorly

5. Jaw ClosingDisc displaced anteriorly

6. Disc Remains DislocatedDisc displaced anteriorly

7. Jaw ClosedDisc displaced anteriorly

Click

Click

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permanently out of position, the stage is set for continued pain and significant arthritic degeneration of the joint. As the joint becomes more arthritic due to the constant rubbing of bone on bone, the sounds may resemble the rustling of newspaper. The pain is often worse after the jaw works the hardest, i.e. at mealtimes.

Mechanism of TMJ destruction

Stretched LigamentsElongation (stretching) of the ligaments can occur fol-lowing macrotrauma or microtrauma.

When the capsular ligaments are stretched beyond their elastic limit, they remain permanently elongated and distorted. When ligaments are lax, the balance shifts to the muscles for stabilization; and a change occurs in the trajectory of mandibular movement and point of den-tal contact (occlusion). The ligament elongation results in disc movement, which leads to posterior band flatten-ing. This results in reduced condyle-fossa distances and changes in occlusion.

The changes in condyle-fossa relationships result in reduced joint spaces that compress the vascular bed of the retro-discal tissues. The arterial blood flow in this region is the source of synovial fluid for the joint. The synovial fluid is the medium for nutrition of articulating structures as well as the vehicle for waste removal and lubrication. Compression of these structures results in inflammation — breaks in the glycosaminoglycan structure occur, the disc surface cracks, and synovial fluid is lost.

Inflammatory ResponseFollowing microtrauma or macrotrauma, when the con-dyle and temporal surface translate over the disc, pieces of collagen and glycosaminoglycan may tear off the edges of the disc and then enter the joint space. Synovial fluid is lost from the disc (the primary storage site of synovial

Scanning electron microscope of TMJ disc

Courtesy of Dr. Kurt D. Stormberg

Cortex

Pain

Thalamus

Mast cell

Trigger Normaldirection

Trigeminalnucleus

Endothelium

5-HT Inhibitorysite

Antidromic

conductionOrthodormic

conduction

VasodilationPlasma Extravasation

Brainstem

C-fos

Orthogonal misalignment

Plane of Occlusion

Courtesy of James Carlson

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fluid) and then produces free radicals that initiate an in-flammatory response with the introduction of mast cells to the area.

The mast cells release serotonin (5HT), which regulates the release of inflammatory neuropeptides (i.e., calcitonin gene related peptide, bradykinins, and substance P). These travel up the nociceptive nerve endings of the joint to the brain stem. An increase in tonus of the elevator muscles occurs and results in increased load on the TMJs.

The increased load on the TMJ resulting from in-creased muscle tonus is magnified when there are uneven vectors of force on the TM joints. This happens when the plane of occlusion is uneven. The forces are heavier on the low side (the side that occludes first) than on the high side.

This overload of supporting tissue may result in par-tial or total disc displacement with or without reduction.

Whole Body ConnectionChronic forward head posture results in increased load. Correct head posture with the center of the ear sitting directly over the center of the shoulder results in a head that weighs 10 pounds, producing a 10 pound load on the spine and its tissue. However, for each inch forward, the load increases by 10 pounds.8 Thus, a head posture that is three inches forward of normal would result in a

30-pound increase in load on the spine and its tissues. Abnormal anterior rotation of ilium causes anterior rota-tion of mandible.

Mandibular cant of the head (mediolaterally) pro-duces a shift in the spine and consequently a shift in the pelvis with rotation that may produce symptoms in the low back. If the mandible is canted (mediolaterally), then C2 is also canted and the patient will not be able to rotate his or her head equally left to right.

SummaryTMJ anatomy comprises the bones, ligaments, tendons and muscles of the region. In addition, an understand-ing of the joint spaces, articular disc, synovial tissues and fluids, and the role of proteoglycans is necessary to un-derstand the factors involved in TMJ health and disease. With an understanding of TMJ anatomy and pathology, it is possible to examine, diagnose, and triage patients. Following appropriate patient selection, patients can be treated with oral appliances.

Endnotes1 American Dental Association. Future of Dentistry:

Dental and Craniofacial Research. Ch.7, 116. Available at www.ada.org. Accessed November 2006.

2 American Dental Association. Future of Dentistry: Dental and Craniofacial Research. Ch.7, 116. Available at www.ada.org. Accessed November 2006.

3 Okeson J. Orofacial Pain: Guidelines for Assessment, Diagnosis, and Management. 1996; Quintessence.

4 Ibid.5 Lundh H, Westesson P L, Kopp S. A three-year

follow-up of patients with reciprocal temporoman-dibular joint clicking. Oral Surg Oral Med Oral Pat. 1987;63(5):530–533.

6 Oleson J, Felt-Hansen PT. The Headaches. 2005.7 Pertes R, Gross S. Clinical Management of Tem-

poromandibular Disorders and Orofacial Pain. 2005; Quintessence.

8 Cailliet R. Head and Face Syndromes. Ed. 1.

DisclaimerThe authors of this course have no commercial ties with the sponsors or the providers of the unrestricted educational grant for this course.

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Questions

1. Up to ________ of the population has at least one sign or symptom of temporomandibular joint disorder (TMD).a. 25 percentb. 45 percentc. 75 percentd. 85 percent

2. A healthy joint is a prerequisite for ________.a. poor masticationb. poor mobilityc. successful examsd. successful restorative work

3. The TMJ is the ________ joint in the body.a. least complexb. most complexc. oldestd. softest

4. The TMJ provides for ________movements.a. hinging and slidingb. hinging and rotatingc. rotating and slidingd. None of the above

5. The TMJ is classified as a com-pound joint, requiring the presence of ________.a. at least two bonesb. at least three bonesc. at least three bones and five tendonsd. none of the above

6. The articular disc is composed of ________.a. dense fibrous connective tissueb. hyaline cartilage interspersed with

connective tissuec. bone with a cartilage coatingd. none of the above

7. From an anterior view the articular disc is thicker ________.a. mediallyb. distallyc. superiorlyd. inferiorly

8. When the mandible opens, the inferior joint space ________.a. opens more anteriorlyb. opens more posteriorlyc. opens more superiorlyd. none of the above

9. The precise shape of the articular disc depends upon the morphology of ________.a. the mandibular fossab. condylec. hyoid boned. a and b

10. The retrodiscal tissue is ________. a. located posterior to the articular discb. highly innervatedc. highly vasculard. all of the above

11. The articular surfaces of the condyle and mandibular fossa are lined with ________.

a. hyaline cartilageb. hyaline bonec. osteoidd. dense fibrous connective tissue

12. Compared to fibrous connective tissue, hyaline cartilage ________.a. is more susceptible to the effects of agingb. is more liable to break downc. has less ability to repaird. all of the above

13. Synovial fluid in the TMJ acts as a medium providing metabolic requirements to the surrounding tissues.a. Hyaline fluidb. Synovial fluidc. Cellular matrixd. none of the above

14. The synovial fluid ________.a. acts as a lubricantb. helps to minimize frictionc. is too thick to move aroundd. a and b

15. No barrier exists between the synovium and the fluids present in the joint spaces because ________.a. there is no epithelium or basement membraneb. there is no space for fluid to pass through anywayc. chemicals in the region ensure the fluid passes

through by osmosisd. none of the above

16. GAGs can produce a cushion to compressive loads by ________.a. causing the cartilage to imbibe

extracellular waterb. causing the cartilage to imbibe intracellular waterc. causing the cartilage to imbibe extra and intracel-

lular waterd. none of the above

17. Requirements for healthy cartilage include ________.a. plenty of waterb. proteoglycansc. a collagenous massd. all of the above

18. The functional ligaments that support the TMJ are ________.a. the collateral ligamentsb. the capsular ligamentc. the temporomandibular ligamentd. all of the above

19. The accessory ligaments for the TMJ are ________.a. stylomandibularb. sphenomandibularc. a and bd. none of the above

20. The muscles of mastication include the ________.a. temporalis and masseter b. lateral and medial pterygoidc. anterior and posterior digastricd. all of the above

21. Temporomandibular disorders result from ________.a. macrotraumab. microtraumac. a and bd. none of the above

22. Microtrauma occurs as a result of ________.a. sustained adverse loadingb. sudden forcesc. repetitive adverse loadingd. a and c

23. Inflammation of the joint space can be the result of ________.a. unresolved ligamentous insertion injuries due

to traumasb. unresolved tendinous insertion injuries due

to traumasc. resolved tendinous insertion injuries due

to traumasd. a and b

24. Capsulitis and synovitis may be associated with ________.a. a disc displacementb. hypermobilityc. dislocationd. all of the above

25. If a disc is reduced, ________.a. it cannot be recapturedb. it can be recapturedc. it is removable

26. In cases with disc displacement without reduction, ________.a. the ligaments have not been stretched enoughb. the posterior lateral ligaments have been

severely stretchedc. the tendons are suspectd. none of the above

27. Mast cells release ________ as part of the inflammatory response.a. serotoninb. prolactinc. nothingd. a and b

28. Disc surface cracks can occur as a result of ________.a. compressionb. elasticityc. depressiond. all of the above

29. Bradykinin and substance P are ________.a. inflammatory neuropeptidesb. inflammatory biopeptidesc. important for joint lubricationd. none of the above

30. Abnormal rotation of the ilium can cause ________.a. posterior rotation of the mandibleb. posterior retrusion of the maxillac. anterior rotation of the mandibled. any of the above

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Educational Objectives1. List and describe the functional anatomy of the temporomandibular joint (TMJ).

2. List and describe what makes the TMJ a unique joint.

3. List and describe TMJ pathology.

Course EvaluationPlease evaluate this course by responding to the following statements, using a scale of Excellent = 5 to Poor = 0.

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Objective #2: Yes No

2. To what extent were the course objectives accomplished overall? 5 4 3 2 1 0

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6. Please rate the instructor’s effectiveness. 5 4 3 2 1 0

7. Was the overall administration of the course effective? 5 4 3 2 1 0

8. Do you feel that the references were adequate? Yes No

9. Would you participate in a similar program on a different topic? Yes No

10. If any of the continuing education questions were unclear or ambiguous, please list them.

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11. Was there any subject matter you found confusing? Please describe.

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12. What additional continuing dental education topics would you like to see?

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